Showing papers on "Equilibrium mode distribution published in 1986"

Highly selective evanescent modal filter for two-mode optical fibers.

Abstract: Efficient and selective coupling between a single-mode fiber and the LP11 mode of a double-mode fiber is demonstrated in an evanescent directional coupler. With greater than 90% coupling to the LP11 mode, suppression of the coupled power to the lower-order LP01 mode was measured to be at least 24 dB. This device has application as a modal filter for the construction of in-line all-fiber optical components.

High power mode conversion for linearly polarized HE11 hybrid mode output

Abstract: Efficient plasma heating by ECR-wave irradiation requires axisymmetric, narrow, pencil-like millimetre wave beams with well-defined polarization. The linearly polarized gaussian-like HE11, mode satisfies these conditions best. This quasi-optical hybrid mode can be generated from TE0n gyrotron mode compositions by the two multi-step mode conversion processes: (1) ΣTE0n to TE01 to TE11 to HE11 or (2) ΣTE0n to TE01 to TM11 to HE11. The first scheme has the advantage that the converters can all be made without bends, allowing an arbitrary choice and fast change of the polarization plane. The second scheme does not exhibit this advantage, but it is more suitable at very high frequencies (e.g. 140GHz) because efficient TE01-to-TM11 transducers can be made considerably shorter than serpentine TE01-to-TE11 mode converters. This paper presents computations on mode converter systems of the first type at 70GHz and of both types at 140GHz (ID = 27 · 8 mm for 200kW transmission lines). The structure of wall perturbati...

Differential mode loss and mode conversion in passive fiber components measured using the chromatic launching and the central spot far field techniques

Abstract: Mode spectra launched conventionally and using the chromatic launching (CL) method are analyzed using the central spot far field (CSFF) method. This is applied to study the differential mode loss and mode conversion properties of passive optical fiber components manufactured using the fused-head-end (FHE) technique.

Mode competition of the gyrotron under high efficiency operating conditions

Abstract: Mode competition — interaction between a mode and another mode — is due to the non-linearity of the relativisitc factor γ. At the beginning of a multimode oscillating, the behavior of the multimode oscillating is only dependent on the ratio of mode frequency and relativistic cyclotron frequency and is in agreement with that described by single mode theory. In non-linear domain mode interaction depends on both amplitudes of A1 and A2 and phase difference Δi of the two modes. The main effect of mode interaction is that excitation of the parasitic mode suppresses growth of the operating mode.

The influence of mode partition fluctuations in nearly single longitudinal mode lasers

Abstract: A simple relationship between the mode ratio of a two-mode laser and an empirical mode partition coefficient is derived. The effects of the mode ratio of a two-mode laser on the bit-error-rate floor of an optical fiber system are calculated, and the power penalties due to mode partitioning in the presence of Gaussian receiver noise are evaluated. The analysis provides a simple way to calculate the effects of mode ratio on the sensitivity of optical receivers.

Mode coupling in single-mode fiber: the advantage of using higher-order spatial-distortion-function harmonics

Abstract: It is demonstrated that light power may be converted from the guided LP01 mode to the radiative LP11 mode in single-mode optical fiber by using a periodic square-shaped distortion function. Coupling between these modes is measured directly as a function of distortion wavelengths and amplitudes for different optical wavelengths. The beating length between the modes (approximately 0.5 mm) becomes practical (1.5 mm and more) through the use of the higher harmonics of the distortion function.

Single Mode Fibre Characteristics

Abstract: Single mode fibres (having circular symmetry) are now being extensively used in fibre-optic communication systems. In this paper, starting from the definition of a mode, we have discussed the important characteristics of these fibres such as the material and waveguide dispersion, attenuation, near and far-field radiation patterns, splicing and microbending losses, various spot sizes, etc. We have also discussed the commonly-used Gaussian approximation and its limitations.

Development of Equilibrium Mode Distribution (EMD) in a Fiber - A Characterization of the Transient Behavior and Steady State Mandrel (SSM) for Corning Data Broadband Fiber (dBF)

Abstract: Contained in this paper are empirical results leading to a better understanding of the development of a steady state power distribution in an optical fiber, commonly referred to as Equilibrium Mode (Power) Distribution (EMD). First, three terms are defined and the importance of their measurement given: Transient Loss, Steady State Mandrel (SSM) Prescription, and Mode Power Distribution (MPD) Measurement. Second, the results of the transient loss testing and the mandrel wrap experiment, which determined the SSM (a mandrel which can be used for convenient attenuation measurement), are given for 85μm core fiber (Corning Data Broadband Fiber (dBF)). Third, MPD measurements verifying the conclusions drawn concerning the establishment of EMD or steady state are given as a function of fiber length and for various launch conditions.This paper has two primary conclusions. First, by actual measurement of the relative mode power distribution in sample fibers, steady state or EMD has been shown to have been established. Second, a mode filter in the form of a mandrel around which the sample was wrapped five times has been chosen such that the steady state power distribution was reproduced.

Characteristics of a single‐mode fiber beyond the cutoff frequency of the LP11 mode

Abstract: To clarify the basis of the concept of effective cutoff wavelength useful for design of single mode optical fibers, this paper discusses theoretically and experimentally the mode conversion effect due to fluctuation of the fiber structure in addition to the difference of the attenuation constants of the modes. In the two-mode region, the scattering matrix elements of the optical fiber are measured with respect to the power of the LP01 and LP11 modes. Based on the measurement, the wavelength dependence of the mode conversion coefficient h and the mode attenuation αi are determined. Next, the multimode dispersion and excess loss of the two-mode system with mode conversion are related to the parameters h and αi and the significance of the effective cutoff wavelength is discussed. It is found that at frequencies slightly beyond the theoretical cutoff for the measured sample fiber the difference of attenuation constants of two modes is substantial. In addition, since the mode conversion coefficient is small, the degradation of the transmission characteristics due to the higher order mode is reduced, resulting in the effective single mode transmission line. Also found is the condition to be satisfied by h and αi so that the desired transmission characteristics (dispersion and loss) are realized with a necessary length of fiber.

Transmission performance impairment due to degradation of optical spectrum in -1.55 μm DFB laser

Abstract: The dynamic optical spectrum and optical transmission characteristics of a 1.55 μm conventional distributed feedback (DFB) laser with a side mode were analysed. The laser used in the experiment came to operate in two modes although initially it had operated in single-mode. When this laser was directly modulated by setting the bias current around the threshold, the mode switching between a main mode and a side mode was observed to be similar to mode partitioning in Fabry-Perot (FP) lasers. The mode switching affects considerably the bit error rate performance of 113 km single-mode fibre transmission at 140 Mbit/s.

Bandwidth characteristics of optical transmission line constructed with short-length optical fibers

Abstract: This paper clarifies the bandwidth characteristics of a VAD-fabricated optical line constructed with short-length optical fibers. The refractive index profiles of these optical fibers are slightly distorted from the ideal profile. Their bandwidth characteristics are calculated and measured under the overfill mode distribution (OMD) and the equilibrium mode distribution (EMD) excitations. As a result, some of the optical fibers are shown to have extremely narrow bandwidths at the short fiber length under OMD excitation as compared with those under EMD excitation. The concatenation factor of the optical line consequently becomes a smaller value than that of an optical line constructed with long-length optical fibers. In addition, the measurement results of the optical subscriber transmission line field trial are shown to be in good agreement with those obtained in this paper.